Uveal melanoma immunogenomics predict immunotherapy resistance and susceptibility.

Immune checkpoint inhibition has shown success in treating metastatic cutaneous melanoma but has limited efficacy against metastatic uveal melanoma, a rare variant arising from the immune privileged eye. To better understand this resistance, we comprehensively profile 100 human uveal melanoma metastases using clinicogenomics, transcriptomics, and tumor infiltrating lymphocyte potency assessment. We find that over half of these metastases harbor tumor infiltrating lymphocytes with potent autologous tumor specificity, despite low mutational burden and resistance to prior immunotherapies. However, we observe strikingly low intratumoral T cell receptor clonality within the tumor microenvironment even after prior immunotherapies. To harness these quiescent tumor infiltrating lymphocytes, we develop a transcriptomic biomarker to enable in vivo identification and ex vivo liberation to counter their growth suppression. Finally, we demonstrate that adoptive transfer of these transcriptomically selected tumor infiltrating lymphocytes can promote tumor immunity in patients with metastatic uveal melanoma when other immunotherapies are incapable.

Mouse Model of Poorly Differentiated Thyroid Carcinoma Driven by STRN-ALK Fusion.

Chromosomal rearrangements of the ALK gene, which lead to constitutive activation of ALK tyrosine kinase, are found in various cancers. In thyroid cancers, ALK fusions, most commonly the STRN-ALK fusion, are detected in papillary thyroid cancer and with higher frequency in poorly differentiated and anaplastic thyroid cancers. Our aim was to establish a mouse model of thyroid-specific expression of STRN-ALK and to test whether this fusion drives the development of thyroid cancer with a propensity for dedifferentiation. Transgenic Tg-STRN-ALK mice with thyroglobulin-controlled expression of STRN-ALK were generated and aged with or without goitrogen treatment. Thyroids from these mice were subjected to histologic and immunohistochemical analysis. Transgenic mice with thyroid-specific expression of STRN-ALK developed poorly differentiated thyroid tumors by the age of 12 months in 22% of mice without goitrogen treatment and in 36% of mice with goitrogen treatment. Histologically and immunohistochemically, the tumors resembled poorly differentiated thyroid cancers in humans, demonstrating a solid growth pattern with sheets of round or spindle-shaped cells, decreased expression of thyroglobulin, and a tendency to lose E-cadherin. In this study, we report a novel mouse model of poorly differentiated thyroid cancer driven by the STRN-ALK oncogene with phenotypic features closely recapitulating human tumor, and with a more pronounced phenotype after additional thyroid-stimulating hormone stimulation.

Investigation of the Relationship Between Radiation Dose and Gene Mutations and Fusions in Post-Chernobyl Thyroid Cancer.

Background: Exposure to ionizing radiation during childhood is a well-established risk factor for thyroid cancer. However, the genetic mechanisms of radiation-associated carcinogenesis remain not fully understood. Methods: In this study, we used targeted next-generation sequencing and RNA-Seq to study 65 papillary thyroid cancers (PTCs) from patients in the Ukrainian-American cohort with measurement-based iodine-131 (I-131) thyroid doses received as a result of the Chernobyl accident. We fitted linear regression models to evaluate differences in distribution of risk factors for PTC according to type of genetic alteration and logistic regression models to evaluate the I-131 dose response. All statistical tests were two-sided. Results: Driver mutations were identified in 96.9% of these thyroid cancers, including point mutations in 26.2% and gene fusions in 70.8% of cases. Novel driver fusions such as POR-BRAF, as well as STRN-ALK fusions that have not been implicated in radiation-associated cancer before, were found. The mean I-131 dose in cases with point mutations was 0.2 Gy (range = 0.013-1.05 Gy), statistically significantly lower than 1.4 Gy (range = 0.009-6.15 Gy) for cases with fusions (P < .001). No driver point mutations were found in tumors from individuals who received more than 1.1 Gy of radiation. Relative to tumors with point mutations, the proportion of tumors with gene fusions increased with radiation dose, reaching 87.8% among individuals exposed to 0.3 Gy or higher. With a limited study sample size, the estimated odds ratio at 1 Gy was 20.01 (95% confidence interval = 2.57 to 653.02, P < .001). In addition, after controlling for I-131 dose, we found higher odds ratios for gene fusion-positive PTCs associated with several specific demographic and geographic features. Conclusions: Our data provide support for a link between I-131 thyroid dose and generation of carcinogenic gene fusions, the predominant mechanism of thyroid cancer associated with radiation exposure from the Chernobyl accident.

THADA fusion is a mechanism of IGF2BP3 activation and IGF1R signaling in thyroid cancer.

Thyroid cancer development is driven by known point mutations or gene fusions found in ∼90% of cases, whereas driver mutations in the remaining tumors are unknown. The insulin-like growth factor 2 mRNA-binding protein 3 (IGF2BP3) plays an important role in cancer, yet the mechanisms of its activation in cancer cells remain poorly understood. Using whole-transcriptome and whole-genome analyses, we identified a recurrent fusion between the thyroid adenoma-associated (THADA) gene on chromosome 2 and the LOC389473 gene on chromosome 7 located 12 kb upstream of the IGF2BP3 gene. We show that THADA fusion to LOC389473 and other regions in the vicinity does not result in the formation of a chimeric protein but instead leads to strong overexpression of the full-length IGF2BP3 mRNA and protein, increased IGF2 translation and IGF1 receptor (IGF1R) signaling via PI3K and MAPK cascades, and promotion of cell proliferation, invasion, and transformation. THADA fusions and IGF2BP3 overexpression are found in ∼5% of thyroid cancers that lack any other driver mutations. We also find that strong IGF2BP3 overexpression via gene fusion, amplification, or other mechanisms occurs in 5 to 15% of several other cancer types. Finally, we provide in vitro and in vivo evidence that growth of IGF2BP3-driven cells and tumors may be blocked by IGF1R inhibition, raising the possibility that IGF2BP3 overexpression in cancer cells may predict an anti-IGF1R benefit.

Identification of the transforming STRN-ALK fusion as a potential therapeutic target in the aggressive forms of thyroid cancer.

Thyroid cancer is a common endocrine malignancy that encompasses well-differentiated as well as dedifferentiated cancer types. The latter tumors have high mortality and lack effective therapies. Using a paired-end RNA-sequencing approach, we report the discovery of rearrangements involving the anaplastic lymphoma kinase (ALK) gene in thyroid cancer. The most common of these involves a fusion between ALK and the striatin (STRN) gene, which is the result of a complex rearrangement involving the short arm of chromosome 2. STRN-ALK leads to constitutive activation of ALK kinase via dimerization mediated by the coiled-coil domain of STRN and to a kinase-dependent, thyroid-stimulating hormone-independent proliferation of thyroid cells. Moreover, expression of STRN-ALK transforms cells in vitro and induces tumor formation in nude mice. The kinase activity of STRN-ALK and the ALK-induced cell growth can be blocked by the ALK inhibitors crizotinib and TAE684. In addition to well-differentiated papillary cancer, STRN-ALK was found with a higher prevalence in poorly differentiated and anaplastic thyroid cancers, and it did not overlap with other known driver mutations in these tumors. Our data demonstrate that STRN-ALK fusion occurs in a subset of patients with highly aggressive types of thyroid cancer and provide initial evidence suggesting that it may represent a therapeutic target for these patients.

ETV6-NTRK3 is a common chromosomal rearrangement in radiation-associated thyroid cancer.

BACKGROUND: In their previous analysis of papillary thyroid carcinomas (PTCs) from an Ukrainian-American cohort that was exposed to iodine-131 ((131) I) from the Chernobyl accident, the authors identified RET/PTC rearrangements and other driver mutations in 60% of tumors. METHODS: In this study, the remaining mutation-negative tumors from that cohort were analyzed using RNA sequencing (RNA-Seq) and reverse transcriptase-polymerase chain reaction to identify novel chromosomal rearrangements and to characterize their relation with radiation dose. RESULTS: The ETS variant gene 6 (ETV6)-neurotrophin receptor 3 (NTRK3) rearrangement (ETV6-NTRK3) was identified by RNA-Seq in a tumor from a patient who received a high (131) I dose. Overall, the rearrangement was detected in 9 of 62 (14.5%) post-Chernobyl PTCs and in 3 of 151 (2%) sporadic PTCs (P = .019). The most common fusion type was between exon 4 of ETV6 and exon 14 of NTRK3. The prevalence of ETV6-NTRK3 rearrangement in post-Chernobyl PTCs was associated with increasing (131) I dose, albeit at borderline significance (P = .126). The group of rearrangement-positive PTCs (ETV6-NTRK3, RET/PTC, PAX8-PPARγ) was associated with significantly higher dose response compared with the group of PTCs with point mutations (BRAF, RAS; P < .001). In vitro exposure of human thyroid cells to 1 gray of (131) I and γ-radiation resulted in the formation of ETV6-NTRK3 rearrangement at a rate of 7.9 × 10(-6) cells and 3.0 × 10(-6) cells, respectively. CONCLUSIONS: The authors report the occurrence of ETV6-NTRK3 rearrangements in thyroid cancer and demonstrate that this rearrangement is significantly more common in tumors associated with exposure to (131) I and has a borderline significant dose response. Moreover, ETV6-NTRK3 rearrangement can be directly induced in thyroid cells by ionizing radiation in vitro and, thus, may represent a novel mechanism of radiation-induced carcinogenesis.

Thyroid carcinoma-associated genetic mutations also occur in thyroid lymphomas.

Molecular testing for mutations activating the mitogen-associated protein kinase signaling pathway is being used to help diagnose thyroid carcinomas. However, the prevalence of these mutations in thyroid lymphomas has not been reported. Therefore, we studied the prevalence of BRAF, NRAS, HRAS, and KRAS mutations in 33 thyroid lymphomas and correlated the mutational status with the clinical, pathological, cytogenetic, and immunophenotypic findings. Eleven cases were also tested for PAX8/PPARγ translocations. The lymphomas included 25 diffuse large B-cell lymphomas, 6 extranodal marginal-zone lymphomas of mucosa-associated lymphoid tissue type, and 2 follicular lymphomas. Seventeen diffuse large B-cell lymphomas were germinal center type, six non-germinal center type, and two unclassifiable (Hans algorithm). None of the cases had an associated thyroid carcinoma. Mutations of the BRAF gene were identified in six (24%) diffuse large B-cell lymphomas (D594G in three germinal center diffuse large B-cell lymphomas, K601N in two germinal center diffuse large B-cell lymphomas, and V600E in one non-germinal center diffuse large B-cell lymphoma) and of the NRAS gene in two (8%) non-germinal center diffuse large B-cell lymphomas (Q61K and Q61H). BRAF and NRAS mutations were not found in any extranodal marginal-zone lymphomas of mucosa-associated lymphoid tissue type or follicular lymphomas. HRAS and KRAS mutations were not identified in any of the cases, nor were PAX8/PPARγ translocations found. Thus, interpretation of finding a BRAF or NRAS mutation in the thyroid, particularly in preoperative thyroid aspirates, must take into account the differential diagnosis of a lymphoma. In addition to the diagnostic importance, our data also demonstrate that alteration in the mitogen-associated protein kinase pathway may have a role in the pathogenesis of some large B-cell lymphomas of the thyroid with potential therapeutic implications.

Homologous chromosomes make contact at the sites of double-strand breaks in genes in somatic G0/G1-phase human cells.

Double-strand DNA breaks (DSBs) are continuously induced in cells by endogenously generated free radicals and exogenous genotoxic agents such as ionizing radiation. DSBs activate the kinase activity in sensor proteins such as ATM and DNA-PK, initiating a complex DNA damage response that coordinates various DNA repair pathways to restore genomic integrity. In this study, we report the unexpected finding that homologous chromosomes contact each other at the sites of DSBs induced by either radiation or the endonuclease I-PpoI in human somatic cells. Contact involves short segments of homologous chromosomes and is centered on a DSB in active genes but does not occur at I-PpoI sites in intergenic DNA. I-PpoI-induced contact between homologous genes is abrogated by the transcriptional inhibitors actinomycin D and α-amanitin and requires the kinase activity of ATM but not DNA-PK. Our findings provide documentation of a common transcription-related and ATM kinase-dependent mechanism that induces contact between allelic regions of homologous chromosomes at sites of DSBs in human somatic cells.

A reappraisal of the MECT1/MAML2 translocation in salivary mucoepidermoid carcinomas.

The MECT1/MAML2 translocation is identified in a large proportion of mucoepidermoid carcinomas (MEC) of the salivary gland and is an emerging favorable prognosticator. However, there are conflicting data on this translocation's specificity, restriction to low/intermediate MEC, and strength as a prognosticator. We present our experience with the MECT1/MAML2 translocation in a large cohort of MECs to address these issues. We analyzed 55 salivary MEC and 36 potential MEC mimics (24 Warthin tumors, 5 oncocytomas, 3 squamous cell carcinomas, 2 squamoid salivary duct carcinomas, 1 lymphoepithelial cyst, 1 Schneiderian carcinoma ex papilloma) for presence of the MECT1/MAML2 translocation by fluorescent in-situ hybridization (FISH) and real-time RT-PCR. Overall, MECT1/MAML2 translocation was present in 36/55 (66%) of MEC whereas all 36 non-MEC were negative for translocation. Low or intermediate-grade MEC had a higher frequency of translocation (75%) than high-grade MEC (46%) (P=0.039). Translocation positive cases had a better disease-specific survival (log rank P=0.026) although 2 patients still died of disease. Within high-grade MEC, MECT1/MAML2 positive tumors had lower rates of anaplasia (P=0.001), and mitotic counts (P=0.012). Thus, MECT1/MAML2 translocation is highly specific for MEC and imparts a better prognosis. However, it is frequent even within high-grade MEC and can be seen in lethal cases suggesting that translocation status should not supersede conventional parameters. There are 2 distinct subgroups within high-grade MEC, and the translocation negative tumors may actually be more appropriately categorized as another tumor type (such as adenosquamous carcinoma).

Diagnostic use of IDH1/2 mutation analysis in routine clinical testing of formalin-fixed, paraffin-embedded glioma tissues.

Mutations in isocitrate dehydrogenase enzyme isoforms 1 (IDH1) and 2 (IDH2) have been identified in many adult astrocytomas and oligodendrogliomas. These mutations are targeted to specific codons (e.g. R132 in IDH1 and R172 in IDH2), making assays to detect them in clinical specimens feasible. We describe a simple and accurate molecular assay for detection of IDH1/2 mutations on routine formalin-fixed paraffin-embedded tissues. Using this polymerase chain reaction-based assay, we tested 75 glial neoplasms and 57 nonneoplastic conditions that can mimic gliomas including radiation changes, viral infections, and infarcts. Of the gliomas, 37 (49%) were positive for IDH1 or IDH2 mutations; the most common mutation was IDH1 (97%). Two of 12 gangliogliomas were positive for IDH1 mutation, and both had unfavorable clinical outcomes (p < 0.03). None of the nonneoplastic cases were positive for IDH mutations. The assay detected IDH mutations in biopsy material containing mostly glioma and in concomitant near-miss stereotactic core biopsies that were otherwise equivocal for the presence of glioma by light microscopy. These results indicate that testing for IDH1/2 mutations can be effectively performed in a clinical setting and can enhance the accuracy of diagnosis of gliomas when traditional diagnostic methods are not definitive.